1. Early Earth Conditions

2. Origin of Life Beliefs
1. Spontaneous Generation- idea that nonliving material can produce life
ex. People believed decaying meat
produced maggots
ex. Mice suddenly appearing in sacks of
grain
1668- Francesco Redi (Italian physician) disproved spon. gen.

3. Redi’s Spontaneous Generation Experiment

4. Disproving spontaneous generation
Redi disproving spon. Gen. allowed people to believe in biogenesis (idea that living organisms come from other living organisms)
SO HOW DID LIFE BEGIN ON EARTH??
TO GET LIFE YOU NEED TO FORM ORGANIC MOLECULES (CONTAIN CARBON)

5. Early Earth Conditions
SO HOT!!! Due to radiation, volcanoes, friction from colliding meteorites
All eruptions of volcanoes made all gases present (CO2, N2, H2, CO, methane, and ammonia
H2O is present as water vapor b/c it’s so hot!!

6. Early Earth Conditions
About 3.6 byo (billion years ago) earth started to cool and H2O condensed to form liquid H2O
*Rock evidence shows 1st life began then
Led to millions of years of rainstorms to form the oceans
Helps support Miller/Urey experiment

7. Formation of Organic Molecules
1. Believed early atmosphere contained
little free O2
2. Most atmosphere was made of (water
vapor, carbon dioxide gas, nitrogen gas,
methane gas, ammonia, hydrogen gas,
and carbon monoxide
*1938 Alexander Oparin proposed Primordial Soup Theory (says life began in the oceans)

8. Primordial Soup Theory
Oparin said energy from sun, lightning, & Earth’s heat triggered chem rxns. to produce small organic molecules from substances present in Earth’s atmosphere
Then rain washed these molecules into oceans making this primordial soup
1953 Stanley Miller/Harold Urey (American Scientists) wanted to test Oparin’s theory by simulating Earth’s early conditions in the lab

9. Miller/Urey Experiment
1. Mix water vapor (steam) w/ ammonia,
methane gas, and hydrogen gas
2. Send electric current (simulates lighting)
through it
3. Cool gases- which produces a liquid
that simulates rain
4. Collect liquid in flask
5. Results- found several kinds of amino
acids, sugars, & other org. molecules
that supported Oparin’s hypothesis

14. So, how do organic molecules lead to cells??
Evolution of Cells
1st cells- protocells- large structure w/ a membrane that contains the primordial soup & carries out cell division
Believed that prokaryotes evolved from protocells
*Remember there is no free O2 present yet
So, 1st prokaryotes were heterotrophic anaerobes that ate primordial soup

15. Evolution of Cells
So, 1st autotrophic bacteria made food (glucose) by chemosynthesis by releasing energy of inorganic molecules & lived in harsh environments
*Similar to present day archaebacteria that live in hot springs
2nd autotrophic bacteria may have been photosynthesizing prokaryotes which released O2 in the atmosphere
Lightning striking the O2 would have formed O3 (ozone) and allowed more complex organisms (eukaryotes) to thrive

16. Endosymbiont Theory *Believed that eukaryotes evolved from prokaryotes
1960s- Lynn Margulis proposed this theory
She said eukaryotes evolved by symbiotic relationships w/ prokaryotes

18. Evidence to support Margulis’ beliefs
Cyanobacteria & chloroplasts (contain DNA & ribosomes) look similar & can both do photosynthesis
Some bacteria & mitochondria (contain DNA & ribosomes) look similar